Galacto-oligosaccharides (GOS) are non-digestible carbohydrates and versatile food ingredients that possess prebiotic properties (Angus, F., Smart, S. and Shortt, C. 2005. In Probiotic Dairy Products ed. Tamine, A. pp. 120-137. Oxford: Blackwell Publishing). In addition, many other health benefits have been reported for these oligosaccharides including: improvement of defecation, stimulation of mineral absorption, elimination of ammonium, colon cancer prevention, as well as protection against certain pathogenic bacteria infections (Hopkins, M. J. and Macfarlane, G. T. 2003 Appl Environ Microbiol 69, 1920-1927; Shoaf, K., G. L. Mulvey, G. D. Armstrong, and R. W. Hutkins. 2006 Infect Immun 74:6920-8; Macfarlane, G. T., Steed H., Macfarlane S. 2008 Journal of Applied Microbiology 104, 305-44).
The human gastrointestinal tract (GIT) hosts a large bacterial population of 500-1000 different phylotypes that reside in the colon (Ninonuevo, M. R., et al. 2007 Anal Biochem 361,15-23). Among them, Bifidobacterial species are the predominant microbial in the infant GIT, exerting beneficial effects to their host such us immuno-stimulation, human pathogen inhibition, vitamin production, and anticarcinogenic activity, among others (Harmsen, H. J., et al. 2000 J Pediatr Gastroenterol Nutr 30:61-7; Casci, T., et al. 2007 Human Gut microflora in Health and Disease: Focus on Prebiotics. In Functional food and Biotechnology. Ed Taylor and Francis. pp 401-434). Due to these beneficial health effects, Bifidobacteria are considered probiotics and have being increasingly used in functional foods and pharmaceutical products (Stanton, C., et al. 2003. Challenges facing development of probiotics-containing functional foods. In Handbook Fermented Functional Foods, Functional Foods and Nutraceutical Series. CC Press, Boca Raton, Fla. pp 27-58).
The physicochemical characteristics of GOS have enabled them to be incorporated as prebiotic food ingredients in a variety of designed foods (Sako, T., et al. 1999 Int Dairy J 9, 69-80). GOS are of particular interest in confectionary acidic beverage and fermented milk foimulations as they possess increased thermal stability in acidic environments compared to FOS (Watanuki, M., et al. 1996 Ann Report Yakult Central Inst Microbiol Res 16, 1-12). Thus, in the past decade, GOS have also had an increasing application in human food products, including dairy products, sugar replacements and other diet supplements as well as infant formula (Macfarlane, G. T., Steed H., Macfarlane S. 2008 Journal of Applied Microbiology 104, 305-44).
Galacto-oligosaccharides are naturally occurring in human milk, however, commercial GOS preparations are produced by enzymatic treatment of lactose with β-galactosidases from different sources such as fungi, yeast and/or bacteria, yielding a mixture of oligomers with varied chain lengths (Angus, F., supra). Thus, the basic structure of GOS includes a lactose core at the reducing end which is elongated typically with up to six galactose residues. GOS structural diversity dependents on the enzyme used in the trans-galactosylation reaction, and the experimental conditions such as pH and temperature (Dumortier, V., et al. 1990. Carbohydr Res 201:115-23.).
Despite the amount of research claiming GOS bifidogenic effect, the vast majority of studies used commercially available preparations of GOS, containing high concentrations of monosaccharide (i.e. galactose and glucose) and the disaccharide lactose, all remaining reagents of the trans-galactosylation reaction. Notably, in the majority of reported cases, monosaccharides are the preferred substrates for microorganism when available in a mixed carbon source (Saier, M. H. Jr. 1996. Res. Microbiol, 147, 439-587; Bruckner, R. and Titgemeyer, F. 2002 FEMS Microbiology Letters 209, 141-48).